The present invention relates to retaining wall structures for reinforcement of earthen walls and slopes. More particularly, the present invention relates to a retaining wall reinforcement for earthen walls and slopes that includes the use of a secondary layer of geogrid web material overlaying a primary layer of geogrid web material and both being disposed at a predetermined vertical height of the retaining wall face and extending laterally backwardly therefrom into the backfill material.
Retaining walls, steep slopes and embankments of earth often require reinforcement to prevent unacceptable soil movement. Generally, soil reinforcement is required in construction involving roadways, foundations, retaining walls, and the like, in which soils are susceptible to movement. While reinforcement can be accomplished by using high quality, select soil, it is often desired to reuse existing soil at construction sites. In such circumstances, and sometimes even with the use of supplemental select soils, acceptable safety factors require the construction of additional structures to effect stabilization of the soil in the earthen structure.
While some soil stabilization applications use underlayments or layers of sheet materials which are covered with backfill materials, other applications incorporate retaining walls from which single layer sheet materials extend and are covered with backfill materials. The retaining walls are typically constructed of a plurality of blocks which connect together. Some conventional and well-known blocks have bores which receive pins or dowels therein to connect the blocks in vertically adjacent tiers. Other types of blocks have opposing top and bottom surfaces which are often configured for interlocking engagement in order for the wall made of the blocks to be mechanically connected together.
The previously described retaining walls also generally include at least one laterally extending horizontal reinforcing sheet that prevents sliding or rotational failure of the slope. In a typical site construction, the retaining wall includes many vertically spaced-apart sheets extending from the retaining wall into the backfill material. A side portion of the sheet attaches to the wall, such as by being held between adjacent tiers of blocks or by connectors disposed in the wall, and the other side portion extends outwardly and rearwardly from the wall into the backfill material. The backfill material mechanically secures the sheet to the backfill, and thereby secures the retaining wall to the backfill.
Several different types of sheets are well-known to those skilled in the art for use to mechanically stabilize earth as described hereinabove. The sheets are generally woven, knitted, or stitch-bonded textiles or extruded, oriented plastic sheets. The extruded plastic sheets typically are extruded geogrids made from oriented polymer plastics and having relatively large openings or apertures therein defined by longitudinal ribs and transverse bars. While extruded geogrid webs are used to secure retaining walls to backfill materials, the conventional use of a single layer of the extruded geogrid web at a predetermined vertical location in the retaining wall does have certain limitations in use in certain applications. It is believed that some of the limitations may derive from the use of backfill material which is substantially smaller than the apertures such that the geogrid does not satisfactorily mechanically engage the backfill material.
Accordingly, although there is widespread use of geogrid webs to provide a high-strength connection between a retaining wall and the backfill material behind the retaining wall, there is a long-felt need in the art for a geogrid web construction or application that provides a higher strength connection between a retaining wall and the backfill material behind the retaining wall. It is to address this long-felt need that the present invention was discovered and is now directed.
The present invention meets the need in the art for a higher strength connection between a modular block retaining wall and backfill material provided there behind. Briefly described, the present invention provides a retaining wall reinforcement for mechanically stabilized earth structures comprising a plurality of courses of cementations blocks stacked together so as to define a retaining wall, and including a backfill material provided behind the retaining wall. A first layer of geogrid web material having a leading edge and a trailing edge is provided wherein the leading edge is disposed between vertically adjacent blocks at a predetermined vertical height of the retaining wall and the trailing edge extends laterally backward therefrom and to the backfill material so as to be engaged thereby. A second layer of geogrid web material is provided so as to overlay and to contact the first layer of geogrid web material from the leading edge thereof to at least a medial portion thereof between the leading edge and the trailing edge. In this fashion, the use of a primary geogrid web layer having a secondary geogrid web layer positioned thereon and in contact therewith serves to provide an increase in the connection strength between the retaining wall and the backfill material as can be appreciated from the detailed description provided hereinafter.
It is therefore an object of the present invention to provide an improved retaining wall structure for mechanically stabilized earth wherein the connection strength between the modular block of the retaining wall and the soil mass of the backfill material adjacent the retaining wall is significantly increased.
Some of the objects of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying drawings as described hereinbelow.